1. Field of the Invention
The present general inventive concept relates to a charging device and an image forming apparatus using the same, and more particularly, to a charging device capable of stabilizing a charging potential, and an image forming apparatus using the same.
2. Description of the Related Art
Various types of image forming apparatus are available to form an image on a medium, and these are mainly categorized according to a printing method into a dot printer, an inkjet printer, and a laser printer. The laser printer is superior to the dot printer or the inkjet printer, in that it has a faster printing speed, and better printing quality. Therefore, the image forming apparatuses applying a laser printing method are most widely used.
An image forming apparatus using the laser printing method subsequently operates in the steps of primary charge, exposure, development, transferring, and fusing. Such an image forming apparatus adopts an image forming method in which a negative charge is applied to a surface of an organic photoconductive unit (OPC), and the property of the OPC allows a latent image to be written to a drum surface of the OPC via a laser beam emitted from a laser scanning unit (LSU). The toner is then affixed on the latent image which is later developed into a visual image, the image is transferred to a printing medium, and the image is bonded or fixed to the printing medium by heat and pressure. As a result, the above-described printing operation is completed.
The charging process of the printing operation includes electrical-charging a photoconductive medium surface with a negative charge using corona discharge. In specific, the photoconductive medium is charged with the negative charge through a discharge potential voltage of a charging membercharging member which is positioned at a fore end of an exposure area prior to scanning a laser beam. However, the use of the corona discharge alone to charge the electric charge in the charging process would cause ripple due to an inconstant charging voltage. The ripple of the charging potential induces a problem of a defective image output.
FIG. 1 is a waveform view illustrating variation of a charging voltage of a conventional charging membercharging member.
Referring to FIG. 1, a conventional charging device has a ripple having potential difference between 20V and 30V in a process to charge a potential −600V on a surface of a photoconduction medium. The ripple of the charging potential causes to degrade printing quality especially when printing is performed at high speed, or when a high resolution image is printed.
Conventionally, AC power is supplied to an image forming apparatus to obviate such defects, so that a constant surface potential is applied to the photoconductive medium. Although the ripple of the charging potential is improved, a user still experiences inconvenience because it is necessary to use a high AC voltage separately. As additional power devices are required for an image forming apparatus, it is difficult to miniaturize the image forming apparatus. Accordingly, the freedom of design is deteriorated.